1. Field of the Invention
The present invention relates generally to apparatus and methods for coating thin films of selected materials onto various substrates by photochemical vapor deposition. More particularly, the present invention relates to an improved high throughput reactor which makes optimum use of radiation generated within the reactor and provides uniform dispersion of vapor reactants to produce uniform deposited layers.
2. Description of the Background Art
The use of radiation to photochemically induce the deposition of thin layers on various substrates has become a particularly useful technique due to the relatively low temperatures at which deposition can be carried out. Photochemical vapor deposition has wide application to depositing thin films of a variety of materials, such as nitrides, oxides, or sulfides, on numerous substrate materials, such as semiconductor materials, metals, plastics, and glass. Photochemical vapor deposition processes are especially well-suited for treating substrates, such as temperature-sensitive plastics and many compound semiconductor materials, which cannot be subjected to the high temperatures usually required for more conventional thermal vapor deposition techniques.
Photochemical vapor deposition processes are well-suited for use in the fabrication of semiconductor devices and integrated circuits. For example, it is desirable to deposit a thin layer of silicon nitride (Si.sub.3 N.sub.4) onto semiconductor devices as a passivation layer to prevent contamination of the device. In U.S. Pat. No. 4,265,932, which is assigned to the present assignee, there is disclosed an apparatus of the conventional planar geometry comprising a flatbed-type vacuum envelope containing a horizontal heated substrate holder and closed on top by a fused quartz window. Using such an apparatus, a silicon nitride layer is deposited on a silicon substrate using a mercury photosensitized reaction between silane (SiH.sub.4) and ammonia (NH.sub.3). The process is based upon the use of ultraviolet radiation to excite mercury vapor in the reactor to form mercury in an excited state. The excited mercury then collides with the silane and ammonia to produce activated species thereof, which interact to form the desired silicon nitride deposit. The photochemical reactor apparatus disclosed in U.S. Pat. No. 4,265,932 utilizes a horizontal reaction chamber in which a quartz window integral with the top of the reactor is provided. The ultraviolet radiation necessary to induce the photochemical reaction is produced external to the reaction chamber and transmitted through the quartz window into the reaction chamber.
A common problem experienced by known photochemical reactors is the undesirable deposition of the selected compound (e.g., silicon nitride) onto the quartz window. The formation of a deposited layer of an opaque material such as silicon nitride on the quartz window reduces the amount of radiation transmitted into the reaction chamber and as a result decreases the efficiency of the reaction. In U.S. Pat. No. 4,265,932 this problem was overcome by placing a thin sheet of ultraviolet-transparent material over the internal surface of the quartz window. The thin sheet was mounted on rollers so that it could be continually moved across the quartz window to continually provide a fresh portion of the sheet over the quartz window and thereby maintain transmission of radiation through the quartz window at maximum levels.
Other materials which can advantageously be deposited by photochemical vapor deposition at relatively low temperatures are dielectric oxides, as disclosed in U.S. Pat. No. 4,371,587, which is also assigned to the present assignee. The apparatus disclosed in this latter patent is suitable for conducting photochemical vapor deposition onto various substrates, such as semiconductor devices, metal layers, lenses, mirrors and solar cells. The use of the apparatus disclosed in U.S. Pat. No. 4,371,587 is illustrated for the deposition of a layer of silicon dioxide (SiO.sub.2) onto silicon substrates, as in semiconductor device fabrication. This latter apparatus, like the apparatus disclosed in U.S. Pat. No. 4,265,932, includes a flatbed-type reaction chamber having a quartz window in the top through which radiation is transmitted. The substrates are located horizontally within the reaction chamber and the reactant gases are flowed into the chamber through a side wall. The photochemical vapor deposition process may be mercury-sensitized, in which the radiation is absorbed by the mercury atoms to produce excited mercury atoms which then react with an oxygen-containing precursor to produce atomic oxygen which, in turn, reacts with a vapor phase reactant to deposit the desired oxide. Optionally, the required atomic oxygen may be formed by the direct dissociation of the oxygen-containing precursor by radiation of a selected wavelength, in which case mercury sensitization is not used.
Although the apparatus as described in the two above-noted patents are well-suited for their intended purpose, neither reactor is designed to be used in a commercial setting where a large number of substrates must be processed quickly, efficiently, and economically to provide substrates having uniform, high quality films. It would therefore be desirable to provide an improved reactor which is capable of processing a large number of individual substrates at any given time while also providing high quality, uniform deposited layers and improved efficiency and economy.